This application claims the priority of German Application No. 101 02 938.1, filed Jan. 23, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system of pitch-attitude symbols, which can be generated by a head-up display unit of an aircraft. The system of pitch attitude symbols can be displayed by the head-up display as a virtual image in the direction of flight, behind the cockpit screen in a focal (image) plane in front of the background.
During flight at night or in adverse meteorological conditions such as e.g. fog or rain, pilots of an aircraft, e.g. a fixed wing aircraft or a rotary wing aircraft, require so-called flight control aids in the cockpit. These flight control aids are, in particular, indispensable during flight at low altitude. Such flight control aids include a so-called head-up display (HUD) unit.
The term head-up display unit refers to a technical unit by which artificial, i.e. technically generated display contents, are superimposed onto the direct, natural field of vision of the pilot. This HUD unit comprises at least one symbol generator for calculating the required flight symbols, and a projector, which on the basis of the calculation generates the flight symbols and then projects them onto a head-up display (of a display area), i.e. an optically semi-transparent screen which shows a virtual image, e.g. flight symbols. The head-up display corresponds to this display area. This display area (e.g. as an optically semi-transparent screen) enables the pilot to look at the outside world through this display area while at the same time obtaining a generated virtual image in the focal plane, in the direction of view and at a distance from his/her eyes. The virtual image makes it possible for the pilot to view the generated flight symbols and the outside world concurrently, without necessitating accommodation (refocusing the lens of the eye). The virtual image arises outside the cockpit windscreen (from the point of view of the pilot). This virtual image is not based on pixels but as a linear graphic in the focal plane.
The display surface (also called head-up display, HUD) is an essential functional element of the entire HUD unit which is arranged in the direction of vision of the pilot, with the system of flight symbols being mirrored onto said HUD, with the pilot then seeing the flight symbols outside the cockpit windscreen.
In the publication Richard L. Newman, Head-Up-Displaysxe2x80x94Designing the Way Ahead, Avebury Aviation, Ashgate Publishing Ltd., Gower House, Croft Road, Aldershot, Hants GU11 3HR, England, ISBN 0-291-39 811-1 (1995), the contents of which are incorporated by reference herein as non-essential matter, known flight symbols for flight control using a head-up display are explained. Below, preferably the system of flight attitude symbols, i.e. a system of pitch attitude symbols, will be discussed. Any references in the following text to flight attitude, refers specifically to pitch attitude.
The arrangement of the HUD is related to the context of the three spatial axes of an aircraft. The imaginary spatial axis which can be arranged in longitudinal direction of the aircraft, is the longitudinal axis of the aircraft, also known as the longitudinal axis X. When the aircraft is positioned horizontally on the surface of the earth, the longitudinal axis X of the aircraft points to the natural horizon. The pilot""s point of sight is also located on longitudinal axis X. The longitudinal axis X and the natural horizon are almost congruent. This position of the aircraft also applies to horizontal flight. Horizontal flight corresponds to a neutral flight attitude.
In relation to horizontal flight, the head-up display is arranged in the cockpit so that it is positioned in the direction of the longitudinal axis X, i.e. so that the natural horizon can essentially be artificially indicated in the middle of the display area. The natural horizon is indicated by the neutral line (horizon line) within a so-called pitch ladder. This is essentially a graphic symbol (e.g. line symbol). The neutral line of this pitch ladder is always at the same height as the natural horizon. Within the pitch ladder, the HUD also shows the aircraft symbol, indicated by a two-part horizontal bar. The aircraft symbol is located on the longitudinal axis X of the aircraft. The aircraft symbol indicates the fictitious penetration point of the imaginary longitudinal axis X through the HUD. The pilot needs to move the aircraft symbol to the neutral line to move to horizontal flight. When the aircraft leaves horizontal flight, the aircraft symbol acts as a fixed reference mark, with the neutral line of the pitch ladder shifting in relation to the aircraft symbol.
The pitch attitude is thus one of the important items of flight control information which a pilot requires for controlling the air vehicle. As is known, the system of pitch attitude symbols is formed by the neutral line of a pitch ladder and the aircraft symbol being stationary as a reference. The two together form the pitch attitude symbol.
By means of an angular-degree scale which can be shown in addition, the pilot can recognize the pitch attitude of the air vehicle relative to the horizon, from the difference between the aircraft symbol and the neutral line.
The landing approach of an aircraft represents a critical flight phase which requires increased attention and precise pilot action. In view of this it may be sensible to arrange the HUD lower in relation to the fixed longitudinal axis X, i.e. in close proximity to the lower border of the pilot""s field of vision. This would take better account of the typical direction of vision during approach for landing. This poses a problem in that during horizontal flight, both the neutral line and the aircraft symbol, are located above the display area of the HUD. Conventional indication of the pitch attitude is thus no longer possible.
It would be possible to shift the pitch ladder with the neutral line (which up to now was identical to the natural horizon line) below the horizon line too. This would mean giving up the reference to the true, natural horizon. However, this is not customary in the case of aircraft. It could lead to misinterpretation of the true flight attitude (pitch attitude) and thus to the introduction of uncontrolled flight situations.
In an arrangement of the display area of an HUD below the natural horizon (during neutral flight attitude) there is a problem in that the conventional system of pitch attitude symbols is no longer possible, because said system always relates to the horizon.
It is thus the object of the invention, to provide an unequivocal system of pitch attitude symbols for the pilot, for a display area of an HUD, which display area during neutral flight attitude of an aircraft is arranged below the natural horizon.
This object is met in that within the focal plane the system of pitch attitude symbols comprises at least one pitch attitude representation area, arranged in perspective, which pitch attitude representation area can always be arranged parallel to the surface of the earth, wherein the rear edge of the pitch attitude representation area is tiltably fixed in a rear edge axis. And, depending on the pitch attitude of the aircraft, the pitch attitude representation area can be tilted in the focal plane, with the front edge showing the pitch attitude in relation to an angular-degree scale.
The system of pitch attitude symbols has the advantage that its interpretation is intuitive. It has an unconventional appearance so that any danger of mistaking it for conventional elements can be excluded.
The pitch attitude representation area has the advantage that it can be shown in correct perspective, directly relative to the background (terrain and/or sky). Because of this the entire image has a consistent appearance. Furthermore, the perspective representation of the pitch attitude representation area results in optical foreshortening (xe2x80x9ccompressionxe2x80x9d) of the angular area displayed. Thus a relatively large angle can be shown on a small display area of the HUD unit.
The system of pitch attitude symbols is associated with the following advantages: (1) the pitch attitude information does not relate to the horizon; (2) the zero position reference is always situated within the display region; (3) the system of symbols is more coherent than is the case with the state of the art, thus making the display more legible; and (4) the pitch attitude information can be positioned anywhere in the display area.
Advantageously, the pitch attitude representation area can be shown with a zero position reference area, wherein the rear edge of the zero position reference area is fixed and united with the rear edge of the pitch attitude representation area, wherein the zero position reference area is fixed with its front edge indicating the position of the neutral line.
The system of pitch attitude symbols can be freely positioned in the focal plane.
According to a further embodiment, a system of roll attitude symbols can be shown above the system of pitch attitude symbols. The system of roll attitude symbols is represented by a movable line symbol and a fixed triangle symbol.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.